<template>
  <div class="progress-bar" ref="progressBar" @click="progressClick">
    <div class="bar-inner">
      <div class="progress" ref="progress"></div>
      <div class="progress-btn-wrapper" ref="progressBtn"
           @touchstart.prevent="progressTouchStart"
           @touchmove.prevent="progressTouchMove"
           @touchend.prevent="progressTouchEnd"
      >
        <div class="progress-btn"></div>
      </div>
    </div>
  </div>
</template>

<script>
  import {prefixStyle} from 'common/js/dom'

  const progressBtnWidth = 16
  const transform = prefixStyle('transform')

  export default {
    props: {
      percent: {
        type: Number,
        default: 0
      }
    },
    created() {
      this.touch = {}
    },
    methods: {
      progressTouchStart(e) {
        this.touch.init = true
        this.touch.startX = e.touches[0].pageX
        this.touch.left = this.$refs.progress.clientWidth
      },
      progressTouchMove(e) {
        if (!this.touch.init) {
          return
        }
        const moveX = e.touches[0].pageX - this.touch.startX
        const offsetWidth = Math.min(this.$refs.progressBar.clientWidth - progressBtnWidth, Math.max(0, this.touch.left + moveX))
        this._offset(offsetWidth)
      },
      progressTouchEnd() {
        this.touch.init = false
        this._triggerPercent()
      },
      progressClick(e) {
        const rect = this.$refs.progressBar.getBoundingClientRect()
        const offsetWidth = e.pageX - rect.left
        this._offset(offsetWidth)
        this._triggerPercent()
      },
      _offset(offsetWidth) {
        this.$refs.progress.style.width = `${offsetWidth}px`
        this.$refs.progressBtn.style[transform] = `translate3d(${offsetWidth}px,0,0)`
      },
      _triggerPercent() {
        this.$emit('percentChange', this._getPercent())
      },
      _getPercent() {
        const barWidth = this.$refs.progressBar.clientWidth - progressBtnWidth
        return this.$refs.progress.clientWidth / barWidth
      },
      setProgressOffset(percent) {
        if (percent >= 0 && !this.touch.init) {
          const barWidth = this.$refs.progressBar.clientWidth - progressBtnWidth
          const offsetWidth = percent * barWidth
          this._offset(offsetWidth)
        }
      }
    },
    watch: {
      percent(newPercent) {
        this.setProgressOffset(newPercent)
      }
    }
  }
</script>

<style scoped lang="stylus" rel="stylesheet/stylus">
  @import '~common/stylus/variable'
  .progress-bar
    height 30px
    .bar-inner
      position relative
      top 13px
      height 4px
      background rgba(0, 0, 0, 0.3)
      .progress
        position absolute
        height 100%
        background $color-theme
      .progress-btn-wrapper
        position absolute
        left -8px
        top -13px
        width 30px
        height 30px
        .progress-btn
          position relative
          top 7px
          left 7px
          box-sizing border-box
          width 16px
          height 16px
          border 3px solid $color-text
          border-radius 50%
          background $color-theme
</style>
